Add author and publish date to storefront pages underneath the title

functions.php

add_action( 'storefront_page', 'wc_ninja_add_pages_byline', 11 );
function wc_ninja_add_pages_byline() {
	?>
	<div class="author">
		<?php
			echo '<span class="label">' . esc_attr( __( 'Written by', 'storefront' ) ) . ' </span>';
			the_author_posts_link();
			echo "<br>";
			storefront_posted_on();
		?>
	</div>
	<?php
}